1: the copying of something by americans and claiming it as their own
2: the misspelling or misspronunciation of a word by Americans and claiming it correct

1: The American sitcom 'Three's Company' is the Yankification of the British comedy 'Man About The House'
2: color instead of colour, pronouncing aluminium 'aloominum' or lieutenant 'lootenant' not 'leftenent'

Yankification is when American culture and American sentiment is expressed in films, music and other media to such an extent that it becomes nauseating. Films like "Independence Day" and the "Patriot" are prime examples.